Stable Mono- and Dinuclear Organosilver Complexes

Article abstract of DOI:10.1021/acs.organomet.6b00771

A series of mononuclear and dinuclear complexes of silver(I), supported by an N-heterocyclic carbene and bound to sp³-, sp²-, and sp-hybridized carbanions, has been synthesized. Synthetic routes include transmetalation from organozinc, organomagnesium, and organosilicon reagents, as well as the deprotonation of a terminal alkyne. These complexes exhibit greater thermal stability than typical organosilver reagents, permitting spectroscopic and structural characterization. The carbanion-bridged disilver cations feature three-center, two-electron bonding with short Ag···Ag distances. A mononuclear vinylsilver complex releases organic homocoupling products upon thermal decomposition, while mononuclear alkylsilver complexes exhibit nucleophilic behavior, for example, inserting CO₂ to form silver carboxylates.

Full text of DOI:10.1021/acs.organomet.6b00771

Article
pubs.acs.org/Organometallics
Stable Mono- and Dinuclear Organosilver Complexes
Brandon K. Tate,†,§ Abraham J. Jordan,† John Bacsa,‡ and Joseph P. Sadighi*,†
†School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
‡X-ray Crystallography Center, Emory University, Atlanta, Georgia 30322, United States
S
* Supporting Information
ABSTRACT: A series of mononuclear and dinuclear
complexes of silver(I), supported by an N-heterocyclic carbene
and bound to sp3-, sp2-, and sp-hybridized carbanions, has
been synthesized. Synthetic routes include transmetalation
from organozinc, organomagnesium, and organosilicon
reagents, as well as the deprotonation of a terminal alkyne.
These complexes exhibit greater thermal stability than typical
organosilver reagents, permitting spectroscopic and structural
characterization. The carbanion-bridged disilver cations feature
three-center, two-electron bonding with short Ag···Ag
distances. A mononuclear vinylsilver complex releases organic homocoupling products upon thermal decomposition, while
mononuclear alkylsilver complexes exhibit nucleophilic behavior, for example, inserting CO2 to form silver carboxylates.
decarboxylation of silver carboxylates have also been studied in
the gas phase.8
INTRODUCTION
■
The organometallic chemistry of silver has been less explored
than that of its congeners, copper and gold. The study of
organosilver chemistry has been limited in many cases by
thermal instability and photosensitivity. For example, phos-
phine-supported alkylsilver complexes decompose quickly at
room temperature, giving primarily the coupling products of
organic radicals, elemental silver, and free phosphine. Many
organosilver compounds that are stable at room temperature,
such as alkynylsilver compounds and phenylsilver, form
coordination polymers, and low solubility limits their utility.
Under the right conditions, however, organosilver compounds
have been effectively used as sources of carbon-based radicals or
carbanions.1 They are probable intermediates in both
stoichiometric2 and catalytic3 silver-mediated C−C coupling
processes, and have been identified in studies of C−C coupling
reactions in the gas phase.4
Early studies of alkylsilver complexes focused on the
detection of thermal decomposition products. Semerano and
Riccoboni5 first inferred the intermediacy of alkylsilver
compounds in the reaction of tetraalkyllead reagents with
silver nitrate, which produces alkyl dimers and elemental silver.6
Further studies followed, demonstrating silver-mediated C−C
coupling of organomagnesium and organolithium reagents.2d−h
Whitesides and co-workers carried out mechanistic studies7 of
the reaction of Grignard reagents with (phosphine)silver
halides. The results suggested that the observed disproportio-
nation to elemental silver and alkyl homocoupling products
sometimes involves homolysis of Ag−C bonds, with release of
free alkyl radicals, but in other cases proceeds through a
concerted bimolecular process. These studies led to the
development of methods for the silver-mediated synthesis of
cycloalkanes,2a and to a variety of silver-catalyzed C−C
coupling processes.1,3 Alkylsilver complexes produced via the
Complexes of silver with sp2-hybridized carbanions were
among the earlier known organosilver species. Krause and
Schmitz prepared phenylsilver by transmetalation from tin,
lead, or magnesium, isolated it as a complex with AgNO3, and
reported its violent decomposition upon evaporation of
solvent.9 The reaction of phenylmagnesium bromide with
AgBr was likewise reported to form an explosive product.10
Later synthetic routes provided pure, isolable phenylsilver.
Despite its low solubility, this complex reacts with acyl halides
to form a mixture of nucleophilic substitution products and
biphenyl.11 Mesitylsilver12 and 2,4,6-triethylphenylsilver13 are
stable at room temperature in the dark, are soluble in solvents
such as toluene and THF, and have been characterized
crystallographically as tetramers with symmetrically bridging
aryl ligands. The more sterically encumbered 2,4,6-(triphenyl)-
phenylsilver is also stable at room temperature but crystallizes
as a monomer.14 Diarylargentate ions, isolated as lithium salts,
decompose slowly at room temperature.15 Vinylsilver7c,d,16 and
allenylsilver17 compounds have also been studied.
Alkynylsilver complexes are among the oldest known
organometallic species, and have found relatively widespread
synthetic applications.18 The reaction of silver nitrate with
acetylene in basic media, first described by Berthelot in 1866,19
results in the precipitation of silver acetylide, a primary
explosive.20 Complexation of silver acetylide with various
combinations of Ag+, other anions, and ancillary donors results
in a broad array of supramolecular architectures.21 Substituted
acetylides may be prepared under similar conditions22 or from
alkynylmagnesium halides,23 and are generally stable at room
Received: October 4, 2016
© XXXX American Chemical Society
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temperature in the dark. Although they typically exhibit low
solubility in common solvents, alkynylsilver compounds have
served as mildly nucleophilic acetylide sources in the
substitution of acyl halides,24 other activated carbonyls,25 and
alkyl halides.26 Alkynylsilver compounds are also likely
intermediates in catalytic C−C and C−N coupling processes27
as well as in the carboxylation of terminal alkynes.28
Scheme 1. Synthesis of Neutral Organosilver Complexes
Complexes of silver with carbanions bearing electron-
withdrawing groups are relatively stable, and their reaction
chemistry has been more widely investigated. The addition of
silver(I) fluoride to perfluoroolefins, for example, gives rise to
perfluoroalkylsilver compounds,29 which can undergo sequen-
tial carboxylation/alkylation30 or reductive C−C homocou-
pling.31 Perfluoroalkyl and pentafluorophenyl complexes of
silver, which are generally stable at room temperature, can also
be conveniently prepared by treatment of AgF with the
corresponding trimethylsilyl reagent.32,33 Synthetic applications
of perfluoroorganosilver complexes include substitution reac-
tions with acyl halides,34,35 chlorosilanes,35 benzyl bromide,35
and alkyl and aryl iodides,35 and the oxidative transfer of the
perfluoroorganic group to elemental copper or to a wide variety
of elements in groups 12−16.33,35 Other halogens, alkoxy,
amino, and trifluoromethyl substituents enhance the stability of
arylsilver compounds, allowing further investigation of their
structures and reactivity.36 Recently Shen and co-workers37
have prepared N-heterocyclic carbene (NHC)-supported
(difluoromethyl)silver complexes via metathesis of alkoxysilver
precursors with (difluoromethyl)trimethylsilane, demonstrated
silver-mediated difluoromethylation and difluorothiomethyla-
tion of a range of electrophiles, and developed a method for
palladium/silver-catalyzed difluoromethylation of aryl halides.
Silyl-substituted alkyl complexes of silver have also been
structurally characterized.38
1
the separation of byproducts. The ethyl ligand exhibits H
NMR resonances with defined 1H−107Ag and 1H−109Ag nuclear
dipole coupling for both the α and β protons, resulting in two
doublets of triplets centered at δ 0.89 ppm for the methyl
protons (Figure 1a), and two doublets of quartets at δ −0.25
Here we report the preparation of a series of stable
mononuclear and dinuclear complexes of silver with carbanion
ligands featuring sp3-, sp2-, and sp-hybridization, supported by
the NHC ligand 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-
ylidene (5Dipp). We have characterized these complexes using
X-ray crystallography and 109Ag NMR spectroscopy; the
dinuclear complexes exhibit significant and varied intermetallic
interactions. Two of these complexes proved amenable to mass
spectrometric characterization. The mononuclear alkylsilver
compounds react as carbon nucleophiles toward CO2, forming
carboxylates.
1
Figure 1. H NMR (400 MHz, THF-d8) resonances of the (a) CH3
and (b) CH2 protons of the ethyl ligand of 3. Corresponding splitting
diagrams are shown underneath.
ppm for the methylene protons (Figure 1b). Because the two-
bond and three-bond H−109Ag coupling constants are similar
1
[2J(1H−109Ag) = 12.8 Hz, J(1H−109Ag) = 12.1 Hz], the 109Ag
3
RESULTS AND DISCUSSION
■
NMR signal resolves as an apparent sextet (Figure 2a).
Rather than using the expensive dimethylzinc, we chose to
prepare (5Dipp)AgMe (4) from methylmagnesium bromide,
which reacts smoothly with 2 in C6D6 or THF solution
(Scheme 1b). The magnesium halide byproducts were
precipitated as 1,4-dioxane adducts, allowing the isolation of
Terminal Organosilver Complexes. Various synthetic
approaches were employed, including transmetalation from
organozinc and organoaluminum compounds, Grignard
reagents, and a trimethylsilyl derivative, using known silver
precursors (5Dipp)Ag(O-t-Bu) (1) and (5Dipp)AgCl (2)
(Scheme 1). The C−H bond of phenylacetylene proved
sufficiently acidic to protonolyze a silver tert-butoxide.
Collectively, these approaches permit the synthesis of a range
of organosilver complexes.
The preparation of (5Dipp)AgEt (3) via ligand exchange
between 1 and 0.5 equiv of diethylzinc proceeds rapidly and
quantitatively in C6D6 or THF-d8 solution at ambient
temperature (Scheme 1a), as judged by 1H NMR spectroscopy.
Complex 3 can be separated from the hydrocarbon-soluble
bis(tert-butoxy)zinc byproduct by precipitation from THF with
the addition of hexanes, allowing its isolation in 55% yield. The
addition of excess diethylzinc does not impede the reaction or
Figure 2. 109Ag NMR (18.6 MHz) resonances for (a) (5Dipp)AgEt
(3) and (b) (5Dipp)AgMe (4).
B
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4 in 85% yield. We subsequently found39 that the reaction
between a trimethylaluminum solution and 1 affords 4 cleanly
(Scheme 1c), and that the hydrocarbon-soluble byproduct
Me2AlOt-Bu is somewhat more conveniently removed. The 1H
NMR spectrum of 4 in CD2Cl2 solution exhibits a doublet
signal for the methyl protons at δ −1.38 ppm. Because coupling
to the 107Ag and 109Ag nuclei is not resolved, the observed
coupling constant of 10 Hz is presumed an average for the
Deprotonation of phenylacetylene by 1 affords (5Dipp)-
AgCCPh (5) (Scheme 1d). This reaction proceeds rapidly and
quantitatively in C6D6 or THF-d8, as judged by H NMR
spectroscopy. Addition of hexanes to a THF solution of 5
causes its precipitation in 61% yield. Excess phenylacetylene
may be used without adverse consequences.
1
A silver trifluoromethyl complex, (5Dipp)AgCF3 (6), was
prepared by reaction of 1 with (trifluoromethyl)trimethylsilane
in THF (Scheme 1e). Precipitation of the product by addition
of hexanes allowed its isolation in 91% yield. The 19F NMR
spectrum of 6 exhibits distinct 19F−107Ag and 19F−109Ag
nuclear dipole coupling, giving rise to a pair of doublets at δ −
1
coupling of H to the two silver isotopes. Indeed, a slightly
greater coupling constant of 11 Hz is observed for the quartet
resonance in the 109Ag NMR spectrum of 4 (Figure 2b),
consistent with the 15% greater gyromagnetic ratio of 109Ag
relative to 107Ag.40 Complex 4 crystallizes as a monomer with
linear coordination about silver (C−Ag−C = 180.0°) (Figure
3).
2
2
291.9 ppm with J(19F−107Ag) = 92 Hz and J(19F−109Ag) =
106 Hz. The 109Ag NMR spectrum displays a quartet
resonance, again with a silver−fluorine coupling constant of
106 Hz.
The silver-bound carbon nuclei of the terminal organosilver
complexes exhibit 13C NMR signals as pairs of doublets due to
well-resolved coupling to 107Ag and 109Ag, as shown in Table 1.
The 13C NMR signals of the Ag-bound carbons of 6 are further
split into quartets, due to coupling to 19F (3J(13CNHC−19F) = 5
1
Hz, J(13CR−19F) = 368 Hz).
Carbanion-Bridged Disilver Cations. Disilver complexes
were prepared either by treatment of the alkoxide-bridged
precursor {[(5Dipp)Ag]2(μ-O-t-Bu)}+ with a carbanion source
or by the combination of a neutral organosilver species with
equimolar (5Dipp)AgOTf (OTf = trifluoromethanesulfonate),
which serves as a ready source of [(5Dipp)Ag]+ (Scheme 3).
Figure 3. Solid-state structure of 4, shown as 50% probability
ellipsoids. Hydrogen atoms omitted for clarity. Selected bond lengths
(Å) and angles (deg): Ag1−C1, 2.114(3); Ag1−C15, 2.076(3); C1−
Ag1−C15, 180.0; N1−C1−N1, 108.7(3).
Scheme 3. Synthesis of Carbanion-Bridged Disilver Cations
Treatment of a suspension of (5Dipp)AgCl in C6D6 with
vinylmagnesium bromide resulted in a clear solution within
seconds, indicating rapid consumption of the sparingly soluble
1
starting complex. A H NMR spectrum recorded 15 min after
the addition of vinylmagnesium bromide exhibited broad
signals at δ 6.59, 5.78, and 5.74 ppm, assigned to the vinylsilver
complex. Traces of 1,3-butadiene, the vinyl homocoupling
product, were also detected, and the deposition of elemental
silver soon became visibly apparent. After 24 h, the integration
1
of H NMR signals against an internal standard suggested
nearly complete conversion to free 5Dipp (>95%), with 1,3-
butadiene formed in at least 80% yield41 (Scheme 2). Because
of its thermal instability, this vinylsilver complex was not
isolated.
Both methyl-bridged42 and alkynyl-bridged43 disilver cations
have been generated in the gas phase by collision-induced
dissociation of the corresponding carboxylate-bridged precur-
sors; alkynyl-bridged cations can also be generated from neutral
alkynylsilver(I) complexes by electrospray impact.43 The
reactions of these complexes with allyl iodide to form new
C−C bonds have been studied using both mass spectrometry
and density functional theory. Analogous complexes of gold(I)
Scheme 2. Decomposition of Inferred Vinylsilver Complex
Table 1. 13C NMR Data for Donor Carbons of Monosilver Complexes (5Dipp)AgR
compd
R
δ(13CNHC), ppm
1J(13CNHC
−
107/109Ag), Hz
δ(13CR), ppm
1J(13CR−107/109Ag), Hz
3
4
5
6
Et
214.6
213.4
210.1
209.6
100/115
111/129
156/181
152/175
1.4
−15.7
122.3
154.0
129/149
120/138
194/224
272/314
Me
CCPh
CF3
C
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with bridging carbanions have been studied extensively,44 and
are likely intermediates in gold-catalyzed processes.45
The disilver cations feature three-center, two-electron
bonding, characterized by short Ag−Ag distances, nonlinear
geometry about each silver center, and 109Ag−107Ag nuclear
dipolar coupling (see Table 2). This structural motif was
Table 2. 109Ag NMR Data for [(LAg)2R]+ Complexes
a
compd
R
δ (109Ag), ppm
J(109Ag−107Ag), Hz
8
Et
Ph
681.2
728.4
55
76
9
10
11
Me no signal detected
CCPh 673.9
18
a
Chemical shift relative to 4.00 M AgNO3 in D2O.
previously observed in the hydride-bridged disilver complex
{[(5Dipp)Ag]2(μ-H)}+,46 and has been postulated in studies of
hydrido-, alkyl- and aryldisilver cations in the gas phase.8f,h
−
The ethyl-bridged {[(5Dipp)Ag]2(μ-Et)}+BF4 (8) was
prepared by ligand exchange of 7 and 0.5 equiv of diethylzinc
in THF (Scheme 3a). Precipitation of 8 by the addition of
hexanes results in a 90% yield. The (5Dipp)Ag fragments of 8
are equivalent in solution on the NMR time scale. Although
coupling to silver is observed for both the α and β protons of
the bridging ethyl ligand, the two isotopes of silver do not give
Figure 4. (a) 109Ag and (b) 109Ag{1H} NMR spectra (18.6 MHz,
1
rise to well-resolved couplings in the H NMR spectrum. The
2
3
CD2Cl2) of 8. J(109Ag−1H) ≈ J(109Ag−1H) ≈ 7 Hz; J(109Ag−107Ag)
= 57 Hz. Insets show rationalization of the pattern as the coincident
signals arising from the two 109Ag-containing isotopologues.
1
two-bond and three-bond H−109Ag couplings in 8 are of
approximately equal magnitude, and coincidentally roughly
equal to the vicinal 1H−1H coupling (2J(1H−107/109Ag) ≈
3J(1H−107/109Ag) ≈ 3J(1H−1H) ≈ 7 Hz), resulting in 1H NMR
signals resembling a sextet for the ethyl α protons at δ 0.64
ppm and a quintet for the β protons at δ 0.17 ppm. The 109Ag
NMR spectrum of 8 features an apparent triplet of sextets
(Figure 4a), reflecting the roughly 7 Hz 1H−Ag coupling
observed in the 1H NMR spectrum as well as substantial
We synthesized the methyl-bridged complex {[(5Dipp)Ag]2-
(μ-Me)}+OTf− (10) by treatment of the terminal analogue 4
with 1 molar equivalent of (5Dipp)AgOTf in CH2Cl2 at −35
°C (Scheme 3b). The complex may also be prepared39 by
treatment of 7[OTf] with less than 1 equiv of trimethylalumi-
num at −35 °C (Scheme 3c); the very soluble byproducts
Me2AlOt-Bu and MeAl(Ot-Bu)2 are easily separated from 10.
Although cold reaction conditions are required in both routes
to prevent the formation of [(5Dipp)2Ag]+ and Ag0, the
dinuclear complex 10 is stable at ambient temperature. The
methyl ligand exhibits a singlet in the 1H NMR spectrum of 10,
lacking the 1H−107/109Ag coupling observed for 4 as well as the
ethyl-bridged analogue 8. We were unable to detect a 109Ag
NMR signal for 10. However, the triangular structural motif
was confirmed by crystallography (Figure 5c). The Ag···Ag
distance of 2.7061(16) Å is nearly the same as in ethyl-bridged
complex 8.
1
109Ag−107Ag coupling (J(109Ag−107Ag) = 56 Hz). H-decou-
pling reduces the 109Ag NMR signal of 8 to an apparent triplet
(Figure 4b). This signal is more properly described as a singlet
arising from the homonuclear 109Ag2 isotopologue, and a
superimposed doublet arising from the heteronuclear
109Ag107Ag isotopologue. Complex 8 crystallizes with a
triangular Ag−C−Ag structure featuring a Ag···Ag distance of
2.7091(8) Å, considerably shorter than twice the van der Waals
radius for silver of 1.72 Å (Figure 5a),47 and similar to the
distances found in silver amidinate dimers.48
The phenyl-bridged disilver complex {[(5Dipp)Ag]2(μ-
Ph)}+BF4 (9) was prepared by treatment of 7 with
−
The disilver phenylethynyl complex {[(5Dipp)Ag]2(μ-
CCPh)}+BF4 (11) was synthesized via the deprotonation of
−
diphenylzinc in THF (Scheme 3a) and precipitated in 86%
yield by the addition of hexanes. As for 8, the (5Dipp)Ag
fragments of 9 are equivalent according to NMR spectroscopy,
and its solid-state structure (Figure 5b) likewise features a
triangular Ag−C−Ag core. Interestingly the Ag···Ag distance of
2.8168(4) Å in 9 is somewhat longer than in 8, yet the
109Ag−107Ag coupling is greater (J(109Ag−107Ag) = 76 Hz). The
Ag−C distances in turn are somewhat shorter than in 8. In
principle, a weak donation from the phenyl π-system to a
vacant Ag−Ag σ* orbital (Figure S21) would weaken the direct
metal−metal interaction slightly, while strengthening the Ag−C
interactions and a through-bond component of the
109Ag−107Ag coupling. This explanation is speculative, however,
and other factors likely play a role.
phenylacetylene by 7 in THF (Scheme 3d). The single set of
NHC resonances observed in its 1H NMR spectrum suggests a
symmetrically bridging phenylethynyl ligand, but the solid-state
structure displays an asymmetric σ,π-bound arrangement. An
analogous gold complex, bearing the supporting ligand IDipp
[1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, also denoted
IPr], exhibits a similar solid-state structure.
Its 1H NMR spectrum likewise featured resonances for
equivalent NHC ligands, consistent with an averaged structure
on the NMR timecale.45g Recently Bertrand and co-workers
reported a phenylacetylide-bridged dicopper cation, supported
by a cyclic alkylaminocarbene (CAAC) ligand. This complex
likewise exhibits equivalent carbene resonances in solution but
D
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Figure 5. Solid-state structures of 8, 9, and 10, shown as 50% probability ellipsoids. Hydrogen atoms omitted for clarity.
distinctly asymmetric σ,π-binding to the two copper centers in
the solid-state structure.49
Two crystallographically distinct molecules, one of which is
shown in Figure 6, are present in the asymmetric unit of 11. In
alkynyls, with distances of 2.552(14) Å to the carbanionic
carbon and 3.040(12) Å to the phenyl-substituted carbon. The
intermetallic distances are 3.033 Å.55
Complex 11 exhibits an apparent triplet in its 109Ag NMR
spectrum, again actually a singlet and coincident doublet. At 18
Hz, the 109Ag−107Ag dipolar coupling of 11 is considerably
smaller than that of 8 (55 Hz) and 9 (76 Hz). Although
differences in solvent and ligation should be borne in mind, the
chemical shift of 673.9 ppm is intermediate between the values
reported for the [(η2-1-hexyne)]silver(I) cation (990 ppm) and
the corresponding σ-(1-hexynyl)silver(I) (416 ppm) in a
weakly donating solvent.56
In light of the importance of mass spectrometry to early
studies of carbanion-bridged disilver cations,42,43 we sought to
obtain electrospray ionization (ESI) mass spectra of complexes
8−11. To date, we have been unable to obtain satisfactory mass
spectra of ethyl-bridged 8 and methyl-bridged 10, possibly
because of their sensitivity in solution to oxidation and
hydrolysis. The more robust phenyl- and phenylacetylide-
bridged cations 9 and 11, however, gave rise to intense parent
ion peaks consistent with the calculated patterns, as shown in
Figure 7.
Reactivity of Alkylsilver Complexes with CO2. The
insertion of CO2 into Ag−C bonds is inferred from several
silver-catalyzed carboxylations28,57 but has been difficult to
study in isolation due to the transient nature of the organosilver
intermediates in these processes. Because of their generally
greater thermal stability, the reactivity of Cu−C35 and Au−C36
bonds toward CO2 has been more thoroughly studied.
Anticipating nucleophilic behavior, we investigated the
reactivity of the NHC-supported organosilver compounds
toward CO2. Complex 3 reacts cleanly with CO2 (1.0 bar) in
CD2Cl2 solution, undergoing complete conversion to (5Dipp)-
AgO2CEt (12) within 16 h at ambient temperature (Scheme
4). Evaporation of volatiles allows isolation of 12 in analytical
purity. Complex 4 reacts more slowly with CO2. After 92 h
under CO2 (1.0 bar) in THF-d8, 79% conversion to the known
complex (5Dipp)AgO2CMe58 is observed, while 12% of 4 is
unreacted and two unidentified new species represent 9% of the
observed [(5Dipp)Ag] resonances, as quantified by integration
Figure 6. One of the two crystallographically distinct molecules of 11
in the asymmetric unit, shown as 50% probability ellipsoids. Hydrogen
atoms omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ag1−Ag2, 3.3707(7); Ag1−C28, 2.061(5); Ag2−C28, 2.177(5);
Ag2−C29, 2.468(5); Ag1−C1, 2.092(5); Ag2−C1A, 2.094(5);
C28−C29, 1.223(8); Ag1−C28−Ag2, 105.3(2).
contrast to the gold and copper analogues described above, the
intermetallic distances in 11 (3.3774(6) and 3.2894(6) Å) are
shorter than two van der Waals radii of the metal, albeit only
slightly: A recent review sets ca. 3.44 Å as the distance within
which an argentophilic interaction should be considered
present.50 In fact, the π-bound silver center is not equidistant
from the two alkynyl carbon atoms but lies distinctly closer to
the terminal carbon, resulting in a T-shaped binding mode. The
η2-binding of organic alkynes and of metal alkynyls to
copper(I) and silver(I) fragments has been reviewed.51 For
side-bound acetylides bound to silver(I), differences in Ag−C
distances on the order of 0.1 Å have been calculated when the
donor ligand is a gold acetylide,52 and observed crystallo-
graphically for some,53 but not all,54 complexes bearing
bis(alkynyl)titanocenes as ligands. A more pronounced differ-
ence, and an arrangement qualitatively similar to that in 11,
occurs in the solid-state structure of [(Me3P)2Ag]+[Ag-
(CCPh)2]−: Each silver cation binds to two silver-bound
1
of H NMR signals against an internal standard.
The alkynyl complex 5, the trifluoromethyl complex 6, and
the bridging complexes 8−11 exhibited no reactivity toward
carbon dioxide in solution at ambient temperature. Because the
reactivity of metal−carbon bonds with CO2 tends to correlate
with their Lewis basicity,59 we speculate that ethyl complex 3
reacts more readily than methyl complex 4 simply because of
the inductive effect of the −CH3 substituent on the silver-
bound carbon. In this view the less basic alkynyl or
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terminal alkyl complex results in the clean formation of a silver
carboxylate.
EXPERIMENTAL SECTION
■
General Considerations. Unless otherwise indicated, manipu-
lations were performed in an MBraun glovebox under an inert
atmosphere of purified nitrogen (NexAir), or in sealable glassware on a
Schlenk line under an atmosphere of argon (NexAir). Glassware and
magnetic stir bars were dried in a ventilated oven at 160 °C and were
allowed to cool under vacuum.
Dichloromethane (BDH), diethyl ether (EMD Millipore Omni-
solv), hexanes (EMD Millipore Omnisolv), and THF (EMD Millipore
Omnisolv) were sparged with argon for 30 min prior to first use and
dried over 3 Å molecular sieves (1/16 in., Alfa-Aesar). Anhydrous
benzene (EMD Millipore Drisolv) and anhydrous pentane (EMD
Millipore Drisolv) were stored over 3 Å molecular sieves. Dichloro-
methane-d2 (Cambridge Isotope Labs) was dried over calcium hydride
overnight, vacuum-transferred to an oven-dried sealable flask, and
degassed by successive freeze−pump−thaw cycles. Tetrahydrofuran-d8
(Cambridge Isotope Labs) and benzene-d6 (Cambridge Isotope Labs)
were dried over sodium benzophenone ketyl, vacuum-transferred to an
oven-dried sealable flask, and degassed by successive freeze−pump−
thaw cycles. Deuterium oxide (Cambridge Isotope Labs) was used as
received.
Carbon dioxide (NexAir) was passed through phosphorus
pentoxide (Sigma-Aldrich) to ensure dryness. Phenylacetylene
(Sigma-Aldrich) and (trifluoromethyl)trimethylsilane (Sigma-Aldrich)
were dried by passing through activated alumina. Diethylzinc (Acros, 1
M in hexanes), 4,4′-dimethylbiphenyl (Sigma-Aldrich), diphenylzinc
(Strem), methylmagnesium bromide (Strem, 3 M in diethyl ether),
and vinylmagnesium bromide (Sigma-Aldrich, 0.70 M in THF) were
used as received. Compounds 1,46 2,60 7,46 7[OTf],46 and (5Dipp)-
AgOTf60 were prepared according to published procedures.
1H, 13C, 19F, and 109Ag NMR spectra were obtained at the Georgia
Institute of Technology NMR Center using a Bruker DSX 400 MHz
spectrometer or a Varian Vx 400 MHz spectrometer. 1H and 13C
NMR chemical shifts were referenced with respect to solvent signals
and are reported relative to tetramethylsilane. 109Ag NMR chemical
shifts were referenced with respect to an external solution of 4.00 M
silver nitrate (Alfa-Aesar) in deuterium oxide (defined as δ 0 ppm). 19F
NMR chemical shifts were referenced to external neat hexafluor-
obenzene (Alfa-Aesar, δ −164.90 ppm) and are reported with respect
to trichlorofluoromethane.
Figure 7. ESI mass spectra of complexes 9 (a) and 11 (b) in THF
solution, positive ion mode. Insets are expanded to show the
theoretical and observed patterns for the parent ion peaks.
Scheme 4. Reaction of 4 with CO2
Infrared spectra were collected using microcrystalline samples on a
Bruker Alpha-P infrared spectrometer equipped with an attenuated
total reflection (ATR) attachment. Samples were exposed to air as
briefly as possible prior to data collection.
Mass spectra were obtained from THF solutions of the complexes
using a Micromass (Watters) Quattro LC triple quadrupole mass
spectrometer, scanning from m/z = 150 to 1500 Da in positive ion
mode.
trifluoromethyl groups, or the bridging carbanions in [Ag2R]+
cores, are kinetically deactivated toward CO2 insertion. This
lack of reactivity is somewhat surprising, however, in light of
processes reported earlier in which the insertion of CO2 into
analogous silver−carbon bonds seems necessary.28,30 Further
investigation will be needed to establish the reactive species in
such processes, and to broaden the scope of this reactivity.
Elemental analyses were performed by Atlantic Microlab in
Norcross, Georgia.
(5Dipp)AgEt (3). A solution of diethylzinc (1.0 M in hexanes, 0.21
mL, 0.21 mmol) was added dropwise to a solution of 1 (0.200 g, 0.350
mmol) in THF (2 mL). The solution was stirred for 10 min, and then
hexanes (15 mL) was added, causing the product to slowly crystallize.
The crystals were allowed to grow for 3 days at −35 °C. The
precipitate was collected on a fritted glass filter by vacuum filtration,
washed with hexanes (3 × 2 mL), and dried in vacuo for 30 min,
affording 3 as a white powder (0.111 g, 0.194 mmol, 55%). Compound
3 hydrolyzes readily in the presence of atmospheric moisture. 1H
NMR (400 MHz, THF-d8): δ (ppm) 7.34 (mult, 2H, para−CH), 7.24
(mult, 4H, meta−CH), 3.99 (s, 4H, NCH2), 3.19 (sept, J = 6.9 Hz, 4H,
CH(CH3)2), 1.38 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.32 (d, J = 6.9
CONCLUSION
■
A bulky N-heterocyclic carbene ligand supports a series of
terminal carbanion-bound silver complexes, as well as a series of
carbanion-bridged disilver cations (Scheme 3). These series
include donor carbons featuring sp3-, sp2- and sp-hybridization.
Most of these complexes, notably including simple neutral
alkyls, proved stable at ordinary temperatures. This stability
probably reflects the rather inert silver−carbene bonding. The
silver vinyl complex, which decomposes readily to silver(0) and
1,3-butadiene at ordinary temperatures, represents a key
exception to this stability. The dinuclear cations include several
examples of three-center, two-electron systems featuring Ag−
Ag interactions, as well as an alkynyl-bridged disilver complex
with a T-shaped coordination mode. Insertion of CO2 into a
3
Hz, 12H, CH(CH3)2), 0.89 (approximate dtd, J(1H−109Ag) = 12.1
3
3
Hz, J(1H−107Ag) = 10.7 Hz, J(1H−1H) = 8.0 Hz, 3H, CH2CH3), −
0.25 (approximate dqd, 2J(1H−109Ag) = 12.8 Hz, 2J(1H−107Ag) = 11.4
3
Hz, J(1H−1H) = 8.0 Hz, 2H, CH2CH3). 13C{1H} NMR (100 MHz,
F
DOI: 10.1021/acs.organomet.6b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
THF-d8): δ (ppm) 214.6 (approximate dd, J(13C−109Ag) = 115 Hz,
J(13C−107Ag) = 100 Hz, NCAg), 147.5 (ortho-C), 136.5 (ipso-C),
129.7 (para-C), 124.6 (meta-C), 54.4 (d, J(13C−107/109Ag) = 4 Hz,
NCH2), 29.4 (CH(CH3)2), 25.4 (CH(CH3)2), 24.0 (CH(CH3)2), 16.9
(d, J(13C−Ag) = 4 Hz, CH2CH3), 1.4 (approximate dd, J(13C−109Ag)
= 149 Hz, J(13C−107Ag) = 129 Hz, CH2CH3). 109Ag NMR (18.6 MHz,
THF-d8): δ (ppm) 790.3 (sextet, J (109Ag−1H) = 12.5 Hz). IR: ν
(cm−1) 2961, 2931, 2837, 1490, 1463, 1275, 1099, 1049 (s), 804, 758.
Anal. Calcd for C29H43N2Ag: C, 66.03; H, 8.05; N, 5.31. Found: C,
65.85; H, 8.21; N, 5.17.
106.5 (J(13C−107/109Ag) = 54 Hz, CCPh), 54.3 (d, J(13C−107/109Ag) =
6 Hz, NCH2), 29.2 (CH(CH3)2), 25.6 (CH(CH3)2), 24.1 (CH-
(CH3)2). IR: ν (cm−1) 3076, 2963, 2929, 2871, 2093 (CC), 1597,
1486, 1464, 1270, 1059, 806, 758, 697, 622, 548, 528, 445. Anal. Calcd
for C35H43N2Ag: C, 70.11; H, 7.23; N, 4.67. Found: C, 69.88; H, 7.24;
N, 4.70.
(5Dipp)AgCF3 (6). (Trifluoromethyl)trimethylsilane (0.155 mL,
1.05 mmol) was added to a solution of 1 (0.500 g, 0.875 mmol) in
THF (4 mL). The mixture was stirred for 30 min, and then hexanes
(15 mL) was added, causing the product to precipitate. The precipitate
was collected on a fritted glass filter by vacuum filtration, washed with
hexanes (3 × 2 mL), and dried in vacuo for 30 min, affording 6 as a
white powder (0.451 g, 0.795 mmol, 91%). Compound 6 hydrolyzes
readily in the presence of atmospheric moisture. 1H NMR (400 MHz,
CD2Cl2): δ (ppm) 7.46 (t, J = 7.8 Hz, 2H, para−CH), 7.30 (d, J = 7.8
Hz, 4H, meta−CH), 4.06 (s, 4H, NCH2), 3.08 (sept, J = 6.9 Hz, 4H,
CH(CH3)2), 1.35 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.33 (d, J = 6.9
Hz, 12H, CH(CH3)2. 13C{1H} NMR (100 MHz, CD2Cl2): δ (ppm)
209.6 (approximate ddq, J(13C−109Ag) = 175 Hz, J(13C−107Ag) = 152
Hz, J(13C−19F) = 5 Hz, NCAg), 154.0 (approximate qdd, J(13C−19F)
= 368 Hz, J(13C−109Ag) = 314 Hz, J(13C−107Ag) = 272 Hz, CF3),
147.2 (Dipp-ortho-C), 134.9 (Dipp-ipso-C), 130.2, (Dipp-para-C),
124.9 (Dipp-meta-C), 54.4 (d, J(13C−107/109Ag) = 5 Hz, NCH2), 29.2
(CH(CH3)2), 25.3 (CH(CH3)2), 24.1 (CH(CH3)2). 19F NMR (376
MHz, CD2Cl2): δ (ppm) 251.3 (approximate dd, J(107Ag−19F) = 92
Hz, J(109Ag−19F) = 106 Hz). 109Ag NMR (18.6 MHz, CD2Cl2): δ
(ppm) 601.3 (q, J(109Ag−19F) = 106 Hz). IR: ν (cm−1) 2964, 2926,
2869, 1488, 1469, 1272, 1110, 938 (s), 807, 762, 446. Anal. Calcd for
C28H38N2AgF3: C, 59.26; H, 6.75; N, 4.94. Found: C, 59.11; H, 6.78;
N, 5.00.
(5Dipp)AgMe (4). Method A: A solution of methylmagnesium
bromide (3.0 M in THF, 0.30 mL, 0.90 mmol) was added to a
suspension of 2 (0.400 g, 0.75 mmol) in THF (2 mL). The mixture
was stirred until it became clear, less than 5 min. Dioxane (18 mL) was
added and the mixture was stirred for 16 h, inducing precipitation of a
magnesium halides as a white powder, which was removed by filtration
through Celite. Volatiles were removed from the filtrate in vacuo, and
the product was extracted from the residue with CH2Cl2. The extract
was filtered through Celite, the solvent was removed in vacuo, and the
residue was dried in vacuo for 2 h, affording 4 as a white powder (0.341
g, 0.66 mmol, 88%). Diffraction quality crystals were grown by
diffusion of pentane vapor into a solution of 4 in CH2Cl2 at −35 °C
over a period of 3 days. Compound 4 hydrolyzes readily in the
1
presence of atmospheric moisture. H NMR (400 MHz, CD2Cl2): δ
(ppm) 7.45 (t, J = 7.8 Hz, 2H, para-CH), 7.29 (d, J = 7.8 Hz, 4H,
meta-CH), 3.99 (s, 4H, NCH2), 3.13 (sept, J = 6.9 Hz, 4H,
CH(CH3)2), 1.37 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.35 (d, J = 6.9
Hz, 12H, CH(CH3)2), −1.38 (d, J(1H−Ag) = 10 Hz, 3H, AgCH3).
13C{1H} NMR (100 MHz, CD2Cl2): δ (ppm) 213.4 (approximate dd,
J(13C−109Ag) = 129 Hz, J(13C−107Ag) = 111 Hz, NCAg), 147.4 (ortho-
C), 135.7 (ipso-C), 129.6, (para-C), 124.6 (meta-C), 54.1 (d,
J(13C−107/109Ag) = 5 Hz, NCH2), 29.2 (CH(CH3)2), 25.3 (CH-
(CH3)2), 24.1 (CH(CH3)2), −15.7 (approximate dd, J(13C−109Ag) =
138 Hz, J(13C−107Ag) = 120 Hz, AgCH3). 109Ag NMR (18.6 MHz,
CD2Cl2): δ (ppm) 842.1 (q, J(109Ag−1H) = 11.2 Hz). IR: ν (cm−1)
2962, 2926, 2870, 1481, 1467, 1457, 1328, 1265, 1258, 809, 763. Anal.
Calcd for C28H41N2Ag: C, 65.49; H, 8.05; N, 5.46. Found: C, 65.73;
H, 7.89; N, 5.59.
{[(5Dipp)Ag]2(μ-Et)}+BF4− (8). A solution of diethylzinc (1.0 M in
hexanes, 0.10 mL, 0.10 mmol) was added dropwise to a solution of 7
(0.200 g, 0.173 mmol) in THF (2 mL). The solution was stirred for 10
min, and then hexanes (15 mL) was added with stirring, causing the
formation of a white precipitate. The precipitate was collected on a
fritted glass filter by vacuum filtration, washed with hexanes (3 × 2
mL), and dried in vacuo for 30 min, affording 8 as a white powder
(0.171 g, 0.154 mmol, 90%). Diffraction-quality crystals were grown by
diffusion of Et2O vapor into a solution of 8 in CH2Cl2 at −35 °C for
48 h. Compound 8 hydrolyzes readily in the presence of atmospheric
moisture. 1H NMR (400 MHz, CD2Cl2): δ (ppm) 7.40 (t, J = 7.8 Hz,
4H, para−CH), 7.18 (d, J = 7.8 Hz, 8H, meta−CH), 4.02 (s, 8H,
NCH2), 2.92 (sept, J = 6.9 Hz, 8H, CH(CH3)2), 1.28 (d, J = 6.9 Hz,
24H, CH(CH3)2), 1.01 (d, J = 6.9 Hz, 24H, CH(CH3)2), 0.64
(approximate sextet, 2J(1H−109Ag) ≈ 2J(1H−107Ag) ≈ 3J(1H−1H) ≈ 7
Hz, 2H, CH2CH3), 0.17 (approximate quint, 3J(1H−109Ag) ≈
Method B: A solution of 1 (0.069 g, 0.12 mmol) in THF (1.5 mL)
and a solution of trimethylaluminum (3 M in hexanes, 0.027 mL, 0.081
mmol) were chilled to −35 °C. The solution of 1 was added to the
solution of trimethylaluminum, and the resulting mixture allowed to
warm to room temperature with stirring. After 15 min, addition of
pentane (6 mL) caused the formation of a white precipitate, which was
collected on a fritted glass filter by vacuum filtration. The solid was
redissolved in THF (1 mL), layered with pentane (5 mL) and placed
in the freezer at −35 °C for 8 h. The supernatant was decanted by
pipet, and the resulting crystals were dried in vacuo for 1 h to afford the
3
3J(1H−107Ag) ≈ J(1H−1H) ≈ 7 Hz, 3H, CH2CH3). 13C{1H} NMR
(100 MHz, CD2Cl2): δ (ppm) 208.8 (mult, NCAg), 146.9 (ortho-C),
135.0 (ipso-C), 130.0 (para-C), 124.8 (meta-C), 54.4 (approximate
1:1:1 t, J(13C−107/109Ag) = 6 Hz, NCH2), 28.9 (CH(CH3)2), 25.3
(CH(CH3)2), 23.9 (CH(CH3)2), 13.4 (t, J(13C−Ag) = 2 Hz,
CH2CH3), − 1.9 (approximate tt, J(13C−109Ag) = 74 Hz,
J(13C−107Ag) = 64 Hz, CH2CH3). 109Ag NMR (18.6 MHz,
1
title complex (0.052 g, 84%). The H NMR spectrum of the product
matched that of a sample prepared by Method A.
(5Dipp)AgCCPh (5). Phenylacetylene (0.047 mL, 0.42 mmol) was
added to a solution of 1 (0.200 g, 0.350 mmol) in THF (2 mL). The
solution was stirred for 10 min, and then hexanes (15 mL) was added,
causing the product to slowly crystallize. The crystals were allowed to
grow for 3 days at −35 °C. The precipitate was collected on a fritted
glass filter by vacuum filtration, washed with hexanes (3 × 2 mL), and
dried in vacuo for 30 min, affording 5 as a white powder (0.128 g,
0.214 mmol, 61%). Compound 5 is air- and moisture-stable in the
3
CD2Cl2): δ (ppm) 681.2 (approximate t of sextets, J(1H−109Ag) ≈
2J(1H−109Ag) ≈ 7 Hz, J(109Ag−107Ag = 55 Hz). 109Ag{1H} NMR (18.6
MHz, CD2Cl2): δ (ppm) 681.2 (approximate t, J(109Ag−107Ag = 55
Hz). IR: ν (cm−1) 2957, 2929, 2871, 1490, 1462, 1275, 1099, 1056 (s),
803, 756. Anal. Calcd for C56H81N4Ag2BF4: C, 60.44; H, 7.34; N, 5.03.
Found: C, 60.47; H, 7.33; N, 4.91.
1
solid state and in solution. H NMR (400 MHz, CD2Cl2): δ (ppm)
−
7.50 (t, J = 7.8 Hz, 2H, Dipp-para−CH), 7.33 (d, J = 7.8 Hz, 4H,
Dipp-meta−CH), 7.19 (d, J = 7 Hz, 2H, CCPh-ortho−CH), 7.11 (t; J
= 7 Hz; 2H; CCPh-meta−CH), 7.19 (t, J = 7 Hz, 1H, CCPh-para−
CH), 4.05 (s, 4H, NCH2), 3.11 (sept, J = 6.9 Hz, 4H, CH(CH3)2),
1.39 (d, J = 6.9 Hz, 12H, CH(CH3)2), 1.38 (d, J = 6.9 Hz, 12H,
CH(CH3)2). 13C{1H} NMR (100 MHz, CD2Cl2): δ (ppm) 210.1
(approximate dd, J(13C−109Ag) = 181 Hz, J(13C−107Ag) = 156 Hz,
NCAg), 147.2 (Dipp-ortho-C), 135.2 (Dipp-ipso-C), 131.7 (CCPh-
ortho-C), 130.1, (Dipp-para-C), 128.0 (CCPh-meta-C), 127.4 (CCPh-
para-C), 125.7 (CCPh-ipso-C), 124.9 (Dipp-meta-C), 122.3 (approx-
imate dd, J(13C−109Ag) = 224 Hz, J(13C−107Ag) = 194 Hz, CCPh)
{[(5Dipp)Ag]2(μ-Ph)}+BF4 (9). Diphenylzinc (0.023 g, 0.10
mmol) was added to a solution of 7 (0.200 g, 0.173 mmol) in THF
(2 mL). The solution was stirred for 10 min, and then hexanes (15
mL) was added with stirring, causing the formation of a white
precipitate. The precipitate was collected on a fritted glass filter by
vacuum filtration, washed with hexanes (3 × 2 mL), and dried in vacuo
for 30 min, affording 9 as a white powder (0.173 g, 0.149 mmol, 86%).
Diffraction-quality crystals were grown by diffusion of pentane vapor
into a solution of 9 in THF at −35 °C for 48 h. Compound 9
1
hydrolyzes readily in the presence of atmospheric moisture. H NMR
(400 MHz, CD2Cl2): δ (ppm) 7.38 (t, J = 7.8 Hz, 4H, Dipp-para−
G
DOI: 10.1021/acs.organomet.6b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 3. X-ray Crystallographic Parameters and Refinement Data
{[(5Dipp)Ag]2(μ-Et)}+ {[(5Dipp)Ag]2(μ-Ph)}+
{[(5Dipp)Ag]2(μ-Me)}+
{[(5Dipp)Ag]2(μ-CCPh)}+
(5Dipp)AgMe
[BF4]−
[BF4]−
[O3SCF3]−
[BF4]−
empirical formula
C28H41AgN2
1519157
513.50
C112H162Ag4B2F8N8
1519158
C68H97Ag2BF4N4O2
1519159
C56H79Ag2F3N4O3S
1519160
C70H97Ag2BF4N4O2
1519161
a
CCDC number
formula weight
crystal system
space group
2225.59
1305.04
1161.03
1329.06
orthorhombic
Pccn
monoclinic
C2
triclinic
monoclinic
P21/n
monoclinic
P1
̅
P21
crystal size (mm)
0.386 × 0.219 ×
0.145
0.81 × 0.62 × 0.37
0.42 × 0.42 × 0.26
0.22 × 0.12 × 0.10
0.512 × 0.196 × 0.126
a (Å)
10.9650(4)
24.156(7)
12.240(4)
29.519(9)
90
10.22449(11)
16.3504(2)
20.3736(3)
86.8617(10)
79.8545(10)
88.8799(9)
3347.50(7)
2
11.9647(15)
16.135(2)
33.041(4)
90
12.50202(20)
31.8127(5)
17.2528(3)
90
b (Å)
12.6078(3)
c (Å)
19.5211(6)
α (Å)
90
β (Å)
90
104.219(4)
90
91.299(2)
90
99.2266(17)
90
γ (Å)
V (Å3)
90
2698.69(13)
8460(5)
3
6377.1(14)
4
6773.0(2)
4
Z
4
absorption coefficient
0.763
0.745
0.640
0.695
0.637
(mm−1
)
Dcalc (g/cm3)
1.264
1.310
1.295
1.209
1.308
T (K)
100(2)
100(2)
100(2)
100(2)
100(2)
θ (deg)
2.087−29.567
32 554
1.710−29.572
57 223
2.024−29.574
68 935
1.405−24.713
35 281
1.50−29.575
86 841
reflections collected
independent reflections (Rint) 3796 (0.0638)
23570 (0.0283)
23570/81/980
R1 = 0.0394
wR2 = 0.0948
R1 = 0.0433
wR2 = 0.0991
1.37/−0.70
18720 (0.0476)
18720/91/779
R1 = 0.0438
wR2 = 0.1065
R1 = 0.0567
wR2 = 0.1127
1.56/−0.66
10863 (0.137)
10863/811/699
R1 = 0.1350
wR2 = 0.2673
R1 = 0.1965
wR2 = 0.2834
1.46/−1.92
37836 (0.0474)
37836/287/1569
R1 = 0.0510
wR2 = 0.1058
R1 = 0.0638
wR2 = 0.1117
1.08/−0.60
data/restraints/parameter
3796/0/147
R1 = 0.0468
wR2 = 0.1019
R1 = 0.0629
wR2 = 0.1091
1.60/−0.28
final R1 indices [I ≥ 2σ(I)]
R indices (all data)
largest difference peak/hole
(e Å−3
)
goodness of fit
1.087
1.047
1.047
1.157
1.031
a
Crystallographic information files have also been deposited with the Cambridge Crystallographic Database, and are available via the Internet at
http://www.ccdc.cam.ac.uk/
CH), 7.12 (d, J = 7.8 Hz, 8H, Dipp-meta−CH), 6.99 (t, J = 7.5 Hz,
1H, μ-Ph-para−CH), 6.69 (t, J = 7.5 Hz, 2H, μ-Ph-meta−CH), 6.14
(mult, 2H, μ-Ph-ortho−CH), 3.96 (s, 8H, NCH2), 2.82 (sept, J = 6.9
Hz, 8H, CH(CH3)2), 1.22 (d, J = 6.9 Hz, 24H, CH(CH3)2), 0.84 (d, J
= 6.9 Hz, 24H, CH(CH3)2). 13C{1H} NMR (100 MHz, CD2Cl2): δ
(ppm) 208.9 (mult, NCAg), 146.9 (Dipp-ortho-C), 144.74 (t, J(13C−
Ag) = 3 Hz, μ-Ph-C) 136.0 (approximate tt, J(13C−109Ag) = 94 Hz,
J(13C−107Ag) = 81 Hz, μ-Ph-ipso-C), 134.7 (Dipp-ipso-C), 131.5 (μ-
Ph-para-C), 130.0, (Dipp-para-C), 127.7 (t, J(13C−Ag) = 3 Hz, μ-Ph-
C), 124.8 (Dipp-meta-C), 54.3 (approximate 1:1:1 t, J(13C−107/109Ag)
= 3 Hz, NCH2), 28.9 (CH(CH3)2), 25.1 (CH(CH3)2), 24.0
(CH(CH3)2). 109Ag NMR (18.6 MHz, CD2Cl2): δ (ppm) 728.4
(approximate t, J(109Ag−107Ag) = 76 Hz). IR: ν (cm−1) 2956, 2929,
2872, 1490, 1460, 1273, 1098, 1051 (s), 804, 769, 758. Anal. Calcd for
C31H47N2AgO: C, 62.08; H, 7.03; N, 4.83. Found: C, 62.03; H, 6.91;
N, 4.81.
NMR (400 MHz, CD2Cl2): δ (ppm) 7.40 (t, J = 7.8 Hz, 4H, para−
CH), 7.18 (d, J = 7.8 Hz, 8H, meta−CH), 3.98 (s, 8H, NCH2), 2.89
(sept, J = 6.9 Hz, 8H, CH(CH3)2), 1.27 (d, J = 6.9 Hz, 24H,
CH(CH3)2), 0.98 (d, J = 6.9 Hz, 24H, CH(CH3)2), − 0.87 (s, 3H,
AgCH3). 13C{1H} NMR (100 MHz, CD2Cl2): δ (ppm) 208.4
(approximate dd, J(13C−109Ag) = 216 Hz, J(13C−107Ag) = 186 Hz,
NCAg), 146.9 (ortho-C), 134.8 (ipso-C), 130.1, (para-C), 124.9 (meta-
C), 121.4 (q, J(13C−19F) = 319 Hz, O3SCF3), 54.4 (NCH2), 28.9
(CH(CH3)2), 25.4 (CH(CH3)2), 23.9 (CH(CH3)2), − 15.7 (dd,
J(13C−109Ag) = 138 Hz, J(13C−107Ag) = 120 Hz, AgCH3), Ag2CH3 not
detected. 109Ag NMR (18.6 MHz, CD2Cl2): Signal not detected. IR: ν
(cm−1) 2961, 2927, 2872, 1488, 1457, 1267 (s), 1149, 1031, 804, 759,
637 (s). Anal. Calcd for C56H79N4Ag2F3O3S: C, 57.93; H, 6.86; N,
4.83. Found: C, 58.14; H, 6.80; N, 4.89.
Method B: A solution of 7[OTf] (0.089 g, 0.072 mmol) in THF
(1.5 mL) and a solution of trimethylaluminum (3 M in hexanes, 0.016
mL, 0.048 mmol) were chilled to −35 °C. The solution of 7 was added
to the solution of trimethylaluminum, and the resulting mixture
allowed to warm to room temperature with stirring. After 15 min,
addition of pentane (6 mL) caused the formation of a white
precipitate, which was collected on a fritted glass filter by vacuum
filtration. The collected solid was redissolved in THF (1.5 mL),
layered with pentane (4 mL) and placed in the freezer at −35 °C for 6
h. The supernatant was decanted by pipet, and the resulting crystals
were dried in vacuo for 1 h to afford the title complex (0.067 g, 81%).
{[(5Dipp)Ag]2(μ-Me)}+[OTf]− (10). Method A: A solution of 5
(0.050 g, 0.097 mmol) in THF (2 mL) and a solution of
(5Dipp)Ag(OTf) (0.063 g, 0.097 mmol) in THF (2 mL) were chilled
to −35 °C. The (5Dipp)Ag(OTf) solution was added to the solution
of 5 dropwise with stirring. The mixture was allowed to warm to room
temperature. After 15 min, the mixture was filtered to remove traces of
a barely perceptible gray precipitate. Diethyl ether (15 mL) was added
to the filtrate, causing the formation of a white precipitate, which was
collected on a fritted glass filter by vacuum filtration, washed with
diethyl ether (3 × 2 mL), and dried in vacuo for 2 h, affording the
product as a white powder (0.094 mg, 0.081 mmol, 84%). Diffraction-
quality crystals were grown by the diffusion of a layer of Et2O into a
CH2Cl2 solution of 10 at −35 °C over a period of 3 days. Compound
1
The H NMR spectrum of the product matched that of a sample
prepared by Method A.
−
{[(5Dipp)Ag]2(μ-CCPh)}+BF4 (11). Phenylacetylene (0.023 mL,
0.21 mmol) was added to a solution of 7 (0.200 g, 0.173 mmol) in
THF (2 mL). The solution was stirred for 10 min, and then hexanes
1
10 hydrolyzes readily in the presence of atmospheric moisture. H
H
DOI: 10.1021/acs.organomet.6b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(15 mL) was added with stirring, causing the formation of a white
precipitate. The precipitate was collected on a fritted glass filter by
vacuum filtration, washed with hexanes (3 × 2 mL), and dried in vacuo
for 30 min, affording the product as a white powder (0.188 g, 0.159
mmol, 92%). Diffraction-quality crystals were grown by diffusion of
pentane vapor into a solution of 11 in THF at −35 °C for 48 h.
Compound 11 is air- and moisture-stable in the solid state and in
for more information). Using Olex2,61 the structure was solved with
the XT62 or XS63 structure solution program using direct methods and
refined with the XL63 refinement package using least-squares
minimization.
ASSOCIATED CONTENT
* Supporting Information
■
S
1
solution. H NMR (400 MHz, CD2Cl2): δ (ppm) 7.40 (t, J = 7.8 Hz,
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00771.
4H, Dipp-para−CH), 7.25 (t, J = 8 Hz, 1H, CCPh-para−CH), 7.19
(d, J = 8 Hz, 8H, Dipp-meta−CH), 7.12 (t; J = 7.2 Hz, 8 Hz; 2H;
CCPh-meta−CH), 6.65 (d, J = 6.9 Hz, 2H, CCPh-ortho−CH), 4.03 (s,
8H, NCH2), 2.96 (sept, J = 6.9 Hz, 8H, CH(CH3)2), 1.29 (d, J = 6.9
Hz, 24H, CH(CH3)2), 1.05 (d, J = 6.9 Hz, 24H, CH(CH3)2). 13C{1H}
NMR (100 MHz, CD2Cl2): δ (ppm) 207.3 (approximate dd,
J(13C−109Ag) = 233 Hz, J(13C−107Ag) = 201 Hz, NCAg), 147.0
(Dipp-ortho-C), 134.7 (Dipp-ipso-C), 132.9 (CCPh-ortho-C), 130.2,
(Dipp-para-C), 129.3 (CCPh-para-C), 128.4 (CCPh-meta-C), 125.0
(CCPh-ipso-C) 124.8 (Dipp-meta-C), 121.3 (mult, CCPh), 98.5 (mult,
CCPh) 54.4 (approximate 1:1:1 t, J(13C−107/109Ag) = 4 Hz, NCH2),
29.0 (CH(CH3)2), 25.5 (CH(CH3)2), 24.0 (CH(CH3)2). 109Ag NMR
(18.6 MHz, CD2Cl2): δ (ppm) 673.9 (approximate t, J(109Ag−107Ag)
= 18 Hz). IR: ν (cm−1) 2961, 2930, 2871, 1487, 1459, 1272, 1048 (s),
804, 756, 443. Anal. Calcd for C62H81N4Ag2BF4: C, 62.85; H, 6.89; N,
4.75. Found: C, 62.85; H, 6.96; N, 5.76.
X-ray crystallographic data for (5Dipp)AgMe,
{[(5Dipp)Ag]2(μ-Et)}+[BF4]−, {[(5Dipp)Ag]2(μ-Ph)}+-
[BF4]−, {[(5Dipp)Ag]2(μ-Me)}+[O3SCF3]−, and
{[(5Dipp)Ag]2(μ-CCPh)}+[BF4]− (CIF)
NMR spectra of isolated compounds and key reaction
mixtures (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: joseph.sadighi@chemistry.gatech.edu.
■
ORCID
(5Dipp)Ag(O2CEt) (12). A solution of (5Dipp)AgEt (0.120 g,
0.227 mmol) in CD2Cl2 (1.0 mL) in a J. Young NMR tube was
degassed by two freeze−pump−thaw cycles, and the tube was
Joseph P. Sadighi: 0000-0003-1304-1170
Present Address
1
backfilled with carbon dioxide (1.0 bar). After 16 h, the H and 13C
§B.K.T.: Department of Chemistry, University of Illinois at
Urbana−Champaign.
NMR spectra of the product were recorded. The tube was opened to
air, and no more effort was made to maintain an inert atmosphere. The
solution was transferred to a vial, and the volatiles were removed in
vacuo. The residue was dried for 4 h at 40 °C, affording 12 as a white
powder (0.123 mg, 0.216 mmol, 95%). Compound 12 is air- and
moisture-stable in the solid state and in solution. 1H NMR (400 MHz,
CD2Cl2): δ (ppm) 7.46 (t, J = 7.8 Hz, 2H, para−CH), 7.30 (d, J = 7.8
Hz, 4H, meta−CH), 4.08 (s, 4H, NCH2), 3.09 (sept, J = 6.9 Hz, 4H,
CH(CH3)2), 1.95 (q, J = 7.6 Hz, 2H, CH2CH3), 1.36 (d, J = 6.9 Hz,
12H, CH(CH3)2), 1.35 (d, J = 6.9 Hz, 12H, CH(CH3)2), 0.87 (t, J =
7.6 Hz, 3H, CH2CH3). 13C{1H} NMR (100 MHz, CD2Cl2): δ (ppm)
207.8 (approximate dd, J(13C−109Ag) = 247 Hz, J(13C−107Ag) = 205
Hz, NCAg), 180.6 (O2C) 147.2 (Dipp-ortho-C), 135.2 (Dipp-ipso-C),
130.1, (Dipp-para-C), 124.9 (Dipp-meta-C), 54.5 (d, J(13C−107/109Ag)
= 9 Hz, NCH2), 29.4 (CH2CH3), 29.2 (CH(CH3)2), 25.4 (CH-
(CH3)2), 24.1 (CH(CH3)2) 11.1 (CH2CH3). IR: ν (cm−1) 2965, 2920,
2868, 2850, 1727 (CO), 1588, 1488, 1461, 1385, 1275, 1058, 805,
760. Anal. Calcd for C30H43N2AgO2: C, 63.04; H, 7.58; N, 4.90.
Found: C, 62.77; H, 7.64; N, 4.86.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the U.S. National Science Foundation for generous
support of this research (CHE-1300659). We thank Prof. Jake
D. Soper and Mr. Caleb Harris for the use of their IR
spectrometer. We thank Dr. Leslie Gelbaum for assistance with
configuring NMR experiments. Dr. David Bostwick obtained
the mass spectrometric measurements; Mr. Andrew D.
Royappa kindly prepared solutions of 9 and 10 for this
purpose. Finally, we are indebted to the reviewers of our
original manuscript for helpful and insightful suggestions,
particularly regarding ESI-MS for the cations.
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DOI: 10.1021/acs.organomet.6b00771
Organometallics XXXX, XXX, XXX−XXX